# Underline Theorem's 'Theorem' part, not the title

I would like to have two different styles of theorems in my LaTeX document to differentiate between original and unoriginal work. For one I would like the 'Theorem' underlined and the other I would like without extra text decoration (as normal).

I use the amsthm package for theorems usually.

For example I would like two different theorems that look like the following would.

\textbf{Theorem 2.2.} \textit{blah blah blah}

\underline{\textbf{Theorem 2.3.}} \textit{blah blah blah}


Like this?

\documentclass{article}
\usepackage{amsmath}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage[amsmath,thmmarks]{ntheorem}

\makeatletter
\newtheoremstyle{myu}%
\makeatother
\makeatletter
\newtheoremstyle{myn}%
{\item[\hskip\labelsep \ \bf ##1 \theorem@headerfont ##2.]}%
\makeatother

\theoremstyle{myn}
\newtheorem{theoremn}{Theorem} %<-- Normal Theorem Definition
\theoremstyle{myu}
\newtheorem{theoremu}[theoremn]{Theorem}%<-- Underlined Theorem Definition

\begin{document}
\section{Introduction}
Theorems can easily be defined
\begin{theoremn}
Let $f$ be a function whose derivative exists in every point, then $f$
is a continuous function.
\end{theoremn}

\begin{theoremu}
Let $f$ be a function whose derivative exists in every point, then $f$
is a continuous function.
\end{theoremu}

\begin{theoremn}
Let $f$ be a function whose derivative exists in every point, then $f$
is a continuous function.
\end{theoremn}

\begin{theoremu}
Let $f$ be a function whose derivative exists in every point, then $f$
is a continuous function.
%\noindent\underline{\makebox[3mm][l]{Jane Doe}}
\end{theoremu}

\begin{theoremu}
Let $f$ be a function whose derivative exists in every point, then $f$
is a continuous function.
\end{theoremu}
\end{document} • No as you can see for my example, I would like the number underlined also (one continuous line). Apr 3, 2019 at 11:36
• @JoshuaFarrell, I have edited my answer.
– user31034
Apr 3, 2019 at 13:51
• \bf has been a deprecated command for more than 20 years. Apr 3, 2019 at 14:22
• @egreg, Thank you for your warning. It sounds easy to use.
– user31034
Apr 3, 2019 at 14:55